In a food processor, pulse the flour, salt, and sugar to combine.
Add the cold coconut oil. Mix the vinegar with the water and slowly add a tablespoon at a time, just until the mixture holds together when lightly squeezed.
Flatten the dough into a disk (you may need to knead it a bit), and wrap in cling film, and chill for a couple of hours.
Once chilled, take out the dough and let soften up for a couple of minutes. Preheat the oven to 350° F. I like to work in small batches, so I divided mine in half and rolled each half about an 1/8 inch (.30 centimeter) thick. I used a small bowl to cut out 5-inch (12-centimeter) circles, but anything around that size will do.
Press into a muffin pan, and using a fork, poke a few holes in the bottom of the tart. Chill until firm. Bake for 8 to 10 minutes.
For the pumpkin filling, mix all the ingredients together with a whisk until smooth.
Add pumpkin filling to the pre-baked shells, and bake for another 20 to 30 minutes, or until the filling is set but still jiggles.